JPH01120505A - Beam converter - Google Patents

Abstract

PURPOSE:To exactly adjust the axis of the incident luminous flux on an objective lens by providing a prism which has an incident face to refract the incident laser light thereon, a reflection face to reflect the laser light after the refraction and an exit face to refract and emit said laser light and converts the light intensity distribution at the section of the laser light to the title converter. CONSTITUTION:The triangular prism 11 having a refractive index (n) has the prism face 11a to refract the incident laser light (a) thereon, the prism face 11b to refract the laser light (b) after the refraction and the prism face 11c to refract the laser light (c) after the reflection and to emit the same as the laser light (d). The angle between the prism faces 11a and 11c is designated as alpha and the angle between the prism faces 11a and 11b is designated as beta. Then, the laser light (a) enters the point A on the prism face 11a at the incident angle theta1i and the laser light (b) refracted at the refraction angle theta1r enters the point B on the prism face 11b at the incident angle theta2. The laser light (c) reflected at the reflection angle theta2 enters the point C on the prism face 11c at the incident angle theta3. This light is refracted as the emission light of the exit angle theta3i.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam conversion device used in an optical information recording/reproducing device such as an optical disk.

[Conventional technology]

In an optical information recording/reproducing device such as an optical disk, the information recording medium is provided with bit-like unevenness or shading as optical information, these bits are irradiated with laser light, and the optical information is determined from changes in the intensity of the reflected light. is being read.

- Fig. 4 shows the structure of an optical information recording/reproducing device for use on a boat.

In the figure, divergent light emitted from a semiconductor laser 1 is converted into parallel light by a collimating lens 2, and the light emitted from this collimating lens 2 passes through a polarizing beam splitter 3 and a 174-wave plate 4, and then is passed through an objective lens 5. The light is focused on the optical disk 6 as a minute spot. This optical disk 6
The light reflected above is separated by a 174-wave plate 4 and a polarizing beam splitter 3, focused on a photodetector 7, and used as an information signal.

A semiconductor laser such as a double heterojunction laser is generally used as a reading light source in the above-mentioned optical information recording/reproducing device.As shown in FIG. Since the pattern, that is, the light intensity distribution 8 of the beam cross section is elliptical, even after the beam is converted into parallel light by the collimating lens 2, the light intensity distribution 8 of the beam cross section maintains an elliptical shape. The light intensity distribution 8 of the convergence spot 5 is not perfectly circular, and there is a drawback that information cannot be recorded and reproduced accurately.

Conventionally, in order to solve this problem, a beam conversion device has been proposed in which one surface of a triangular prism 9 is used as an entrance surface and the other surface is used as an exit surface, as shown in FIG.

According to this beam conversion device, it is possible to give a magnification to the laser beam only in a plane parallel to the plane of the paper, so that the light intensity distribution 8 in the beam cross section can be converted from an elliptical shape to a perfect circle. In an optical system using one prism, the light intensity distribution can be converted, but the optical axis is bent and the incident axis and the output axis do not coincide. However, when using the beam converter in an optical head of an optical information recording/reproducing device,
If the directions of the optical axes do not match, it becomes difficult to design the optical system and there are many restrictions on the arrangement of parts, which is inconvenient.

Therefore, as shown in FIG. 7, two triangular prisms 9a, 9b are arranged in opposite directions, and each triangular prism 9a,
A beam conversion device has also been proposed in which the optical paths are bent to opposite sides by the beam converter 9b. According to this beam conversion device, since the optical path is bent twice, the incident axis and the output axis become parallel. However, the incident axis and the output axis do not coincide.

Furthermore, as shown in FIG. 8, by arranging two cylindrical lenses 10a and 10b orthogonally and changing the magnification of each cylindrical lens lQa and 10b, the light intensity distribution 8 in the beam cross section can be arbitrarily controlled. A beam conversion device has also been proposed.

[Problem that the invention seeks to solve]

In the optical system using two prisms as shown in FIG. 7, the optical axes are parallel, but the incident axis and the output axis still do not coincide. Also, the seventh
In the example shown in the figure, two prisms are required, which increases the size and weight of the device.

For this reason, it has been difficult to apply it to optical heads of optical information recording and reproducing devices.

When used in such an optical head, etc., the optical system shown in FIG. 8, in which the optical axis does not bend or shift, is most suitable.
In an optical system using two 0b lenses, wavefront aberration must be reduced in order to converge a small spot for recording and reproducing optical information, and the disadvantage is that adjustments to suppress this aberration are extremely difficult. arise. This is because when a cylindrical lens is used, the influence of misalignment between the optical axis and the lens and the tilt of the lens is greater than that of a spherical lens.

Furthermore, the beam converting device shown in FIGS. 6 and 7, which is easy to adjust, is not suitable for an optical head or the like because the optical axis is bent or shifted as described above.

The present invention was devised to solve the above-mentioned problems, and by utilizing refraction and reflection in a prism, it is possible to easily adjust the beam without causing bending or deviation of the optical axis. The purpose is to provide a conversion device.

[Means for solving problems]

In order to achieve the purpose, the beam conversion device of the present invention has an entrance surface on which the laser beam is incident and refracted, a reflective surface that reflects the refracted laser beam, and a beam conversion device that refracts the reflected laser beam and emits it. The present invention is characterized in that it has a prism that has an output surface that converts the cross-sectional light intensity distribution of the laser beam.

[Effect]

In the present invention, a beam of light incident on a prism is refracted by an entrance surface of the prism, reflected by a reflection surface within the prism, and finally refracted and output from an output surface. At this time, the refractive index of the prism, the incident point of Radhe light, the incident angle, the reflection point, the exit point, and the exit angle.

By setting the angle between the entrance surface and the exit surface and the angle between the entrance surface and the reflection surface so as to satisfy certain conditions, the optical axes of the incident light and the reflected light are made to coincide. Further, if total reflection within a prism is used as the reflective surface, loss of light amount can be prevented.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 1 is a block diagram of a beam conversion device according to an embodiment of the present invention.

In the figure, 11 indicates a triangular prism with a refractive index n, and this prism 11 includes a prism surface 11a on which the laser beam a is incident and refracted, a prism surface 11b on which the refracted laser beam is reflected, and a prism surface 11b on which the laser beam after reflection is reflected. It is provided with a prism surface 11C that refracts the laser beam C and emits it as a laser beam d.

In the prism 11, if the angle between the prism surfaces 11a and llc is α, and the angle between the prism surfaces 11a and llb is β, then the laser beam a, which is the incident light, hits the point A on the prism surface 11a at an angle of incidence θ. The laser beam C that is incident and refracted at a refraction angle θl is incident at a point on the prism surface 1111 at an incident angle θ2, and the laser beam C reflected at a reflection angle θ2 is incident at a point C on the prism surface 11c at an incident angle θ5. ．． The laser beam d is incident and refracted, and the laser beam d becomes an output beam with an output angle θ31.

Next, the conditions under which the incident light and the outgoing light become parallel will be explained with reference to FIG.

In the figure, from Snell's law (n is the refractive index) sin
θ++=nS! nθ+r””(1) sin θ3□
=nsln03r...(2) Therefore, θ+r =sin-' (sin θ,,/n)
...-(3) θ3r = sin-' (sin
θ3. /n)...(4) Also, θ2=β+θ1r...[5)π-(
α+β)=02-03r...(6) Therefore, from equations (5) and (6), θ2 is eliminated and α+2β+(θ1r
−θ3. )=π...(7) By the way, since θ31=α−θ, 1 (8), substituting equations (3) and (41, (8) into equation (7) yields.

That is, in the prism 11 of FIG. 1, when the parameters α, β, and n and the incident angles θ and I of the incident light are given, satisfying this equation (9) is the condition for the incident light and the output light to be parallel. It is.

Next, conditions for the optical axes of the incident light and the outgoing light to coincide are determined.

Let the coordinates of points A and C be A (0, 0>, C (L
, 0) and find the coordinates (xo, ya) of point B.

The equation of laser beam C is y=tan(θ1.-θIr)X...
α1y =-tan(θ31-θ3r)(XL)...
・OD, and from this point B (Xo, yo) is...α
However, θ3I: α-θth point, and this point B (xo, yo) is the prism surface 1
1b is a condition for the optical axes of the incident light and the outgoing light to coincide and not deviate.

Further, as shown in FIG. 2, the light beam P having a width of WI which is incident on the prism surface 11a is expanded in the width direction by the prism 11, and the width of the light beam P emitted from the prism surface 11C becomes W2. .

The beam conversion magnification at this time is as follows.

COSθ,,’cosθ31 CO2O3, CO5θth ・　・　・Otsu Next, the embodiment shown in FIG. 1 will be shown.

In the figure, the refractive index n of the prism 11 is 1.5. Angle α between prism surface 11a and llc = 105°, llc 11a
If the angle β formed by the 6llb is 27.2° and the laser beam a is incident on the point A on the prism surface 11a at θ, 1 = 75°, then after being refracted at θ, r = 40.1”, Prism surface 11
It is incident on point B on b at θ, = 67.3', and after being reflected there, it is incident on point C on prism surface 11c with θ, , = 19.
The laser beam d enters at an angle of 5°, and at θ3+=30°, the laser beam d becomes an emitted light parallel to the incident light and exits.

Here, 5irr'(1/n) -5in-'(1/1.5
)=41.8°<67.3°, total reflection occurs at point B on the prism surface 11a.

Also, if the distance between point C and point C is 86.2 (relative value), then from equation (2), the distance between point B and straight line AC is 12
．． It becomes 6.

In this example, the beam is expanded in only one direction, but the magnification is 2.72 times according to formula [F], and according to the principle of retrograde light, if the optical path is reversed, the magnification is 0.393 times. be.

That is, as mentioned above, in this embodiment, the beam can be expanded or contracted in only one direction to convert the beam shape into a circular shape, so it can be used not only for optical heads but also for laser beam printers,
It can also be used in beam conversion devices such as scanners.

Further, by providing two or more reflecting surfaces, the performance of the beam conversion device can be greatly improved.

FIG. 3 shows an example of a hexagonal prism that uses reflection twice, and the laser beam e converted into parallel light by the collimating lens 2 (see FIG. It is reflected at points E and F, and at point G, the laser beam f becomes an outgoing beam whose optical axis coincides with that of the incident beam.

In this way, when there are two or more reflective surfaces, the degree of freedom in design increases, so that the magnification of enlargement and reduction can be increased.

〔Effect of the invention〕

As explained above, in the present invention, a beam of light is refracted and reflected by one prism. By setting the optical conditions of this prism to predetermined values, it is possible to obtain output light that is parallel to the incident light and without axis deviation with a simple configuration. Therefore, when performing adjustment to reduce wavefront aberration in order to converge a small spot for optical information recording and reproduction using the beam conversion device of the present invention, the axis of the light beam incident on the objective lens can be adjusted accurately and This can be done easily.Moreover, since only one prism is required, it is possible to achieve reductions in size, weight, and cost.

Furthermore, if total reflection is used as reflection in the prism, light can be reflected efficiently without forming a separate reflective film or the like.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a beam conversion device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the state of beam conversion, and Fig. 3 is another embodiment of the present invention, which uses reflection twice. A diagram showing a beam conversion device, FIG. 4 is a configuration diagram of a general optical information recording/reproducing device, FIG. 5 is a diagram showing a far field pattern of a semiconductor laser, and FIGS. 6 to 8 are diagrams showing conventional beams. FIG. 2 is a configuration diagram of a conversion device. ■ = Semiconductor laser 2; Collimating lens 3:
Polarizing beam splitter 4: l/4 wavelength plate 5: Objective lens 6 Two optical discs 7: Photodetector
8: Light intensity distribution 9, 9a, 9b, 11.12
Niblism lQa, 101] 'Cylindrical lens a-f: Laser light patent applicant Fuji Xerox Co., Ltd. Agent
Person Masu Kobori (and 2 others) 1st
Figure 3 Figure N4 Figure 5 Figure 6

Claims (1)

[Claims] 1. It has an entrance surface on which the laser beam is incident and refracted, a reflection surface that reflects the refracted laser beam, and an exit surface that refracts and emits the reflected laser beam, A beam conversion device comprising a prism that converts a light intensity distribution in a cross section of the laser beam. 2. The beam conversion device according to claim 1, wherein the prism is a triangular prism and satisfies the following formula. ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ However, θ_1_i: Incident angle θ_3_i: Output angle n: Refractive index of the prism ▲ Numerical formulas, chemical formulas, tables, etc. are available ▼ α: Angle between the incident surface and the exit surface β: Incident Angle x_0 between the surface and the reflecting surface: x component of the reflection point y_0: y component of the reflection point 3, total reflection is used as the reflection in the prism, claim 1 or 2. Beam converting device as described in section.